Study On The High-temperature And Anti-seawater-corrosion Solid Self-lubricating Anti-frictional Nickel Base Materials

Nickel alloys have high-working-temperature and good anti-seawater -corrosion performance. Powder metallurgy(PM) technology, which is applied to make complicated metal base solid self-lubricating composites, can combine nickel alloy and solid lubricants to give excellent anti-friction, wear-resistance and self-lubrication that will satisfy the conditions of high-temperature and seawater. Nickel base high-temperature self-lubricating materials containing sulfur and nickel base anti-seawater-corrosion self-lubricating materials fabricated by PM were studied here. Main results are as follows.The microstructure of materials that were made by directly adding MoS₂ into Ni-20Cr powder consists of metal base and the eutectics of Ni(Cr) and sulfurides. Materials having 20wtï¼…MoS₂ have better mechanical and tribological performance. Their friction coefficients decrease as the environment temperature, sliding speed and load rise when matched to W18Cr4V. As temperature increases, Cr_xS_y formed in the material will soften or melt to produce transforming anti-frictional film on worn surfaces, which leads to the decrease of friction coefficient. Particle abrasion is the main wear type during wear process. It is investigated that, though sulfurides eutectics can soften or melt to form lubrication film in rubbing with YJ2 hardmetal matches, the high valent Cr_xS_y will thermal decompose to lose self-lubricating performance. Thus, materials' friction coefficient firstly decreases, then rises as temperature increases, showing the lowest friction coefficient and the best lubricating conditions at 400℃. Wear increases with temperature. Particle abrasion and oxide abrasion are the main wear types at this time. Oxides produced on the worn surface of YJ2 hardmetals matches have important effects on the anti-friction characteristics.Ni coated MoS₂ can be well prepared by Ni(NO)₃ decomposition -hydrogen reduction techniques. It is good to preserve MoS₂ because of nickel preventing MoS₂ from reacting with chromium element. The microstructure of alloys made by adding Ni coated MoS₂ powder into Ni-Cr alloyed powder consists of three parts of metal base, sulfurides-Ni(Cr) eutectics and MoS₂. It is proposed that these alloys show good anti-friction self-lubricating performance in a wide temperature range since they have both the high-temperature solid lubricant(Cr_xS_y) and the low-temperature solid lubricant (MoS₂).Ni-Cr-Mo alloys produced by vacuum sintering give the best mechanical performance when sintered at 1360℃. It is studied that when hot-pressed Ni-Cr-Mo alloys are further sintering-heat-treated, their mechanical and anti-corrosive performance is significantly improved because of the elimination of detrimental inter-metallic composites and the improvement of Mo element solution strengthening in alloys, which improve the alloy's mechanical and anti-corrosive performances much better than those of alloys by vacuum sintering and single hot-pressing. Tensile strength and elongation of the alloys rise while the sintering-heat-treatment(SHT) temperature goes up, showing best performance at 1300℃/SHT. When the temperature continues to rise to 1330℃, the alloys' tensile strength and elongation go down because of lots of brittle phases having high chromium content appear. For Ni-Cr-Mo alloys by hot-pressing(HP), those alloys with additions of W and Cu elements have the best tensile strength(σ_b=671MPa) and elongation(δ=8.5ï¼…). All of the Ni-Cr-Mo serial alloys prepared by 1300℃/4h SHT give their bestσ_b andδwhile alloys adding with only W element have the highest mechanical performance, withσ_b=721MPa,δ=17.7ï¼…,HB=217.Alloys containing W and Cu elements made by HP or SHT have lower corrosion rate than Ni-Cr-Mo base alloys in the 3.5ï¼…NaCl solution. Alloys containing W and Cu elements made by 1300℃/4h SHT shows the best anti-corrosion, with a corrosion rate of 0.002mm/a. These alloys also have satisfying anti-intercrystal corrosion properties when tested in boiling HNO₃. As to tribological performance, friction coefficients for these three alloys of Ni-Cr-Mo,Ni-Cr-Mo-W and Ni-Cr-Mo-W-Cu by the process of HP-SHT are almost the same while alloys having both W and Cu elements have the lowest friction coefficient and wear rates comparatively.Lower friction coefficient and less wear rate than those of Ni-Cr-Mo -W-Cu base materials can be obtained by making materials studded with high pure graphite and PTFE composites in Ni-Cr-Mo-W-Cu base alloys. It is put forward here that materials studded with PTFE composites can show excellent tribological performance under conditions of high load and low speed. The friction coefficient can reach 0.2. Under high load conditions with both NaCl solution and grease, materials studded with PTFE composites tested have the friction coefficient 0.12 and the wear rate of 7.0×10^-15m³/N·m. This material can be used in some nation-defense projects.